Revert "changing %:z docs"

Author: donBarbos

Doc/library/datetime.rst

@@ -2609,7 +2609,7 @@ convenience. These parameters all correspond to ISO 8601 date values.
 |           | Jan 4.                         |                        |       |
 +-----------+--------------------------------+------------------------+-------+
 | ``%:z``   | UTC offset in the form         | (empty), +00:00,       | \(6)  |
-|           | ``±HH[:MM[:SS[.ffffff]]]``     | -04:00, +10:30,        |       |
+|           | ``±HH:MM[:SS[.ffffff]]``       | -04:00, +10:30,        |       |
 |           | (empty string if the object is | +06:34:15,             |       |
 |           | naive).                        | -03:07:12.345216       |       |
 +-----------+--------------------------------+------------------------+-------+